This invention relates to a papermaking felt, and especially to a paper-making felt which is excellent in duration of elasticity.
In general, a papermaking machine is adapted to squeeze water from a wet web by sandwiching the wet web and the web-carrying felt between a pair of press rolls. Thus, a papermaking felt is subjected to pressure along its path at relatively short intervals, causing the felt to lose elasticity gradually by fatigue due to the repeated compression. Ultimately, the papermaking felt becomes flat, and loses its water-squeezing function. Therefore, for a papermaking felt, the duration of its elasticity is especially important.
In Japanese Patent Application No. 166700/1990, the inventor had proposed previously a papermaking felt which met the above-mentioned demand for duration of elasticity. In that proposal, as shown in FIG. 12, a papermaking felt 30 consists of a ground fabric layer 31 of a woven fabric, a batt layer 32, and a non-woven fabric layer 33. The second batt layer 32xe2x80x2 is accumulated on the non-woven fabric layer 33, and the second non-woven fabric layer 33xe2x80x2 is arranged on the surface of the second batt layer 32xe2x80x2. The non-woven fabric layer 33 and the second non-woven fabric layer 33xe2x80x2 are composed of polyelastomer, which is an elastic material, thereby providing an improvement in the duration of the elasticity of the felt.
Prior efforts to improve the duration of the elasticity of a papermaking felt have encountered problems in papermaking machines of the high speed, high pressure type which have appeared in recent years. The elasticity of the felt could not be sustained satisfactorily over a long period of time, though the duration of elasticity was good when compared with that of former papermaking felts subject to repeated compression at the nip.
An important object of this invention is to solve the above-mentioned problem. The purpose of the invention is to provide a papermaking felt which offers excellent duration of elasticity even in a papermaking machine of high speed and high pressure type.
To address the aforementioned object, a preferred papermaking felt in accordance with the invention comprises a base body and batt layers, and is characterized in that a film layer, formed with elongate ridges having an orientation in the CMD direction, is arranged in the base body, in the batt layers, or between the batt layers. The term xe2x80x9cCMDxe2x80x9d refers to a direction orthogonal to the xe2x80x9cMDxe2x80x9d direction, the latter being the direction in which the papermaking felt of the invention runs. Owing to the film layer, it is possible to run the felt flexibly and smoothly in the winding path in a paper making machine, and the felt resists the tendency to be rendered flat under the nip pressure, which tends to cause fatigue in papermaking felts through repeated compression.
A preferred papermaking felt in accordance with the invention is characterized in that the above-mentioned film layer consists of an elastic material. When the film layer is composed of an elastic material, it causes the initial elasticity of the papermaking felt to be maintained for a longer time.
The elongate ridges of the film layer, oriented in the CMD direction, may be formed by creping, in which case, the structure is such that the elongate ridges may be arranged irregularly, with the height of their peaks and their lengths made random by the forming process itself.
Alternatively, the elongate ridges of the film layer, oriented in the CMD direction, may be formed by embossing, in which case the structure is such that the elongate ridges may be formed easily with a reasonable manufacturing cost.